Bone marrow failure syndromes are associated with a markedly increased risk of developing acute myeloid leukemia (AML). AML arising in the setting of bone marrow failure is associated with distinct clinical and molecular features suggesting that mechanisms of leukemogenesis may be distinct from that seen in de novo AML. As a model for bone marrow failure syndromes in general, mechanisms of leukemogenesis in patients with severe congenital neutropenia (SCN) will be characterized. SCN is an inherited syndrome manifested by severe chronic neutropenia present at birth. Approximately 9% of patients develop AML characterized by a high frequency of chromosome 7 abnormalities. The following specific aims are proposed. Specific Aim 1. We will define the contribution of mutations of the ELA2 gene to the pathogenesis of SCN and development of AML. There is compelling genetic evidence implicating mutations of the ELA2 gene encoding neutrophil elastase (NE) as the cause of most cases of SCN. However, there is no direct proof that expression of mutant NE inhibits granulocytic differentiation, nor have mechanisms of disease pathogenesis been defined. To directly test the hypothesis that ELA2 mutations are causative for SCN, primary hematopoietic progenitor cells will be transduced with lentiviral vectors expressing mutant NE and their effect on granulocytic differentiation characterized. Based on these studies, a mouse model of SCN will be generated, and it will be used to identify mechanisms of disease pathogenesis and leukemogenesis. Specific Aim 2. We will identify genetic progression factors for AML in SCN. Two complementary approaches aimed at gene discovery will be employed. First, the frequency of mutations in candidate genes in samples of AML from patients with SCN will be identified by sequencing. Second, a genome wide scan to identify genetic mutations in any AMLs arising in the mouse model of SCN will be performed, using the expertise and technology developed in project 2. The validity of gene mutations as bona fide progression factors for leukemia will be tested using mouse models. Gain-of-function mutations of the G-CSFR are acquired in approximately one-third of patients with SCN and are strongly associated with the development of AML. The hypothesis that these G-CSFR mutations are an important genetic progression factor for AML in patients with SCN will be tested.